1. Field of the Invention
The invention relates in general to a zoom lens and an image acquisition apparatus incorporating the same, and more particularly to a zoom lens having less than 6 lenses and short back focal length and an image acquisition apparatus incorporating the same.
2. Description of the Related Art
Conventionally, the zoom lens applied in a camera adopts the structure of having three lens groups. However, with the advance in technology and the demand in the market, the design of camera is directed towards slimness, compactness and lightweight. And it is crucial to shorten the back focal length (BFL) of the zoom lens and reduce the number of lens used in the three lens groups.
Besides, the zoom ratio, that is, the ratio of the effective focal length for the telephoto mode to the effective focal length for the wide angle mode, is a significant criterion in assessing the performance of image acquisition. Currently, the digital still camera at least has a zoom ratio of 3.
However, in order to achieve a preferred imaging effect, normally the digital still camera may use up to 10 lenses for the three lens groups, not only causing more restrictions to the structure but also incurring more costs. Therefore, how to reduce the size of the acquisition apparatus and yet maintain the image acquisition ability of the acquisition apparatus and the image quality has become an imminent challenge to the industry. The attempts including using the characteristics of the lenses of the three lens groups, such as the effective focal length, the power and the disposition of the lenses, or replacing multiple spherical lenses by an aspheric lens have been made.